The present invention relates to pressure sensing devices of the type operable to effect making and breaking of electrical contacts in response to quite small changes of a predetermined magnitude in a fluid pressure signal. Devices of this type are employed in numerous applications for electrical control purposes and are commonly employed in clothes washing machines for sensing the water level or head of water in the washing receptacle or tub for controlling an electrically operated water filling valve.
In applications of the aforementioned type, namely, clothes washing machines, the pressure switch is required to sense a change in water level of only a few inches and, therefore a high degree of sensitivity is required. In applications of this type, it has been found convenient to provide the sensitivity by employing a relatively large diameter flexible diaphragm which exhibits sufficient movement in response to the small pressure changes, on the order of an inch of water, or less, to enable the necessary movement to provide actuation of a switch. It has been found desirable in clothes washer pressure switch applications to employ a toggle or snap-acting switch mechanism to prevent arcing and burning of the contacts when the flexible diaphragm moves to a position holding the switch near the trip point. The instability of a snap-acting switch near the trip point enables a very minute amount of switch actuator movement to cause the switch to go overcenter and toggle. The spring biased toggle throws the contacts a sufficient distance under a positive force to provide a very positive making and breaking with sufficient force to resist chattering of the contacts due to any surrounding vibration in the washing machine.
In designing and manufacturing pressure switches for household washing machines for high volume production, it has been desired to minimize the size of the pressure switch for convenience of installation on the washing machine control panel. However, in order to provide the desired movement or sensitivity to the small sensed pressure changes, it has been necessary to employ a sensing diaphragm having a diameter on the order of three inches (76 millimeters) which has resulted in an undesirable bulkiness or excessive overall volume for the Pressure switch. Thus, the required size of the diaphragm has limited the ability of the designer to provide a compact pressure switch for washing machine applications. Heretofore washing machine pressure switches have been commonly provided with a mounting bracket for attachment to the structural housing or control panel of the washing machine; and it has been desired to eliminate this costly extra part in high volume production.
In addition, it has been desired to provide improved ways or means of assembling a pressure switch of the aforementioned type in high volume mass production in a manner that minimizes manufacturing costs and assembly difficulties. Existing appliance pressure switch designs have employed a metal cover or metal clamping band provided about the periphery of the pressure switch for clamping a pair of housing shells together with the peripheral bead of the diaphragm clamped therebetween by deforming the metal cover or band over the pressure switch housing. This assembly technique has proven to be undesirable because once assembled, if leakage about the diaphragm is detected during final testing and calibration, the pressure switch cannot then be disassembled without destruction of the cover or clamping band. This has resulted is costly scrappage or rework in high volume pressure switch production. Accordingly, it has thus been desired to provide a way or means of assembling a pressure switch of the above-described type in high volume production in a manner that provides ease of assembly, reliable sealing of the diaphragm and yet permits nondestructive disassembly of the pressure switch in the event leakage about the diaphragm is detected after assembly.
Furthermore, it has been desired to find a way or means of providing for final calibration of the pressure switch after the unit has been completely assembled.